Multi-user joint RIS channel estimation based on ADMM

Addressing the challenges of high pilot overhead and computational complexity in traditional channel estimation methods for millimeter-wave communication systems aided by reconfigurable intelligent surfaces (RIS), a novel channel estimation algorithm based on the alternating direction method of multipliers (ADMM) for multi-user joint scenarios was proposed. Firstly, leveraging the shared base station (BS)-RIS component within the cascaded channels of different users, the common subspace of user signals was estimated and projected to effectively mitigate noise interference. Secondly, considering the correlation and sparsity of multi-user cascaded channels, an optimization problem for the sparse cascaded channel matrix and common scaling factor matrix was formulated. To solve this non-convex joint optimization problem, the ADMM algorithm was employed to alternately optimize the sparse matrix and the common scaling factor matrix. Simulation results demonstrate that, compared to existing methods, the proposed ADMM-based channel estimation algorithm for multi-user joint scenarios reduces pilot overhead by approximately 50%.